Instrument for determining the weight and active concentration of aerosols

ABSTRACT

An instrument for monitoring industrial atmospheres for determining the weight and active concentration of aerosols, in which the weight of the dust precipitate collected on a filter is determined by the rate of absorption of the radiation of an external alpha particle radioactive source, and the active concentration of the aerosol is determined by measuring the background radiation of the sample. The radiation source and the detector are disposed directly in a gas conduit on both sides of the filter element, on which the aerosol samples are being collected. In order to measure the background radiation of the sample, the radioactive source can be withdrawn from the gas conduit. The instrument is furnished with a collimator in order to reduce the influence of the background activity of the sample on the measurements of the dust concentration.

United states Patent I953 Sigworth ct all [72] Inventors Valentin Grigorievich Babich Leningradskoe shosse. 54, kv. 253;

Alexander Kuzmich Kursky, l j Krasnoselsky per.;5,kv.7'; Konstantin Petrovich Markov, 3 Baltiisky per,4-,korp.' l,kv.8'; Nikoali Vasilievich Ryabov, ZPavIovsky per.,l0a,kv.l0; Konstantin Nikolaevich Stas, 4 ul. Oktyabrskogo polya, l ,kv.20, Moscow, U.S.S.R.

{21 Appl. No. 696,421 [22] Filed Jan. 8, I968 [45] Patented, Jan. 26, I971 [54] INSTRUMENT FOR DETERMINING THE WEIGHT AND ACTIVE- CONCENTRATION OF AEROSOLS 3 Claims, 2 Drawing Figs.

us. Cl 250 435, v 250/833 [5|] Int. Cl ..G0ln 23/06 [50] Field of Search ..i .2 250/43.5D, 44, 43.5R, 83.6(Fl'), 83.3D. 106T [56] References Cited vUNITED STATES PATENTS ALPHA RADIATION sou/ace 6 Attorney-Waters, Roditi and Schwartz ABSTRACT: An instrument for monitoring industrial atmospheres for determining the weight and active concentration of aerosols, in which the weight of the dust precipitate collected on a filter isdetermined by the rate of absorption of the radiation of an external alpha particle radioactive source, and the active concentration of the aerosol is determined by measuring the background radiation of the sample. The radiation source and the detector are disposed directly in a gas conduit on both sides of the filter element, on which the aerosol samples are being collected, In order to measure the background radiation of the sample, the radioactive source can be withdrawn from the gas conduit. The instrument is furnished with a collimator in order to reduce the influence of the background activity of the sample on the measurements of the dust concentration.

DISPLA CEMENT M'CWA/V/SM 7 osrscroe 8 -r'm/vsP0/er MCl/A/V/SM 5 2 a 5 9 PUMP/2 RADIATION INDICATOR ll P 4ECORDR I0 P ATFN'I-El] JAN-P619?! 3.558884 ALPHA AADlAT/ON DISPLACEMENT 7L SOURCE 6\ llama/W344 7 hm/vspakr MEC/M/V/SM 5 Paw/21 RADIATION DETECTOR 8 IND/CA 70/? II I QECORDER /0 in adecreasedsensitivity'ofi measurementstca mgl lmfi P nszriwivtswr FoR-pEmEnMiNitNo r n: 'w monr AND AC1! -1CONCE TR'ATIPJON'GFAERQSO-LS trial atmospheres and, more. ticularly, it relates toinstruments fordeterminingthe we g t'of dust andthe amount of radioactivity per-unit volumeof "the. gas'being' monitored:

' fKnown'are devicesfor measuring the weightandacti'veconccntration-of'aerosols, wherein: aerosolisarnpling iseffected by drawing a test {gas through afilterelement, followed by'determining'thc thickness of the dust precipitate thuslobtained", the dust precipitatethickness being evaluated measuring-the absorption of be'ta' raysemitted by a'radioactive source, in the known devices, dust sampling iscarri'ed out=in ja'gas inlet con duit, while measurements-of the dust precipitate thickness is effected at a distance fromftheas' inlet-conduitwhich'carries saidl radioactive source and. a radiation detector disposed at different sides of the-filterel'e'ment'. 'Inthe beta source',provision-is madefora shield, which makes it possible tomeasurc thebackgrotindradiationofthe dustsarnple bei ngfexamined The 'known devices suffer from a ;riumberof limitations, suchassignificant'duration. of measuriements due to the..necessity of'accumul'ating a substantial amounto'f dust on the-filter element;.-elaborate designofithe radiation detectorand also of the radiation intensity-recorder necessitated by the fact that recourse is hadto low-energy beta rays in order to obtain p ronounced' absorption of the radiation where thedust ipreci'pitate collected on the filter element'is minuteyfailure toaccount for variations in the. thickness of the filter element,

"an'dirindiscriminate recording of dust particles zirrespectivc of the-,par ticle size,.jalthough particles under l0 p. in diameter present maximum health" hazard. Moreover, the known: devices areusually cumbersome and' difficult to operateypariiculaflyunder underground 'rni'rri'ng' conditions, while attempts "to-make the devices compactan d light n weight result ,l'ltsi'snanobject' of the presentiinventi'on -to,proyide a instrument'for measuring the weight and active concentration. of

" aerosolsgwhichthaslhighasensitivity and'precision I ltiSahotherobjeetdf the present. invention toprovide an instrument' for'measuringithe weight and active concentrationof aerosol's that'hasenhancedsensitivity-to dust particles below l-O AI. in diameterwhieh-presenta maximum silicosishazard.

[t'isafurtherobject of the present invention to provide an i'ristrume nt' for measuringythe weight and active concentration -of 'aeroso'ls*which isareliable andwconvenient inoperation munderground mining conditionsandiis-readilytportable In accordance with these and other objects, in thepresent instrument for measuringthe'weight. and active concentration of aerosols aradioaetivesource: and a radiation detector are disposed in a qgas intakingcond'uit, the radioactive source ing placed upstream with= reference-to a-filter-element and eonduit during-aerosol.sarnpling.

1 'An alpha'emitt'er may be used-'to'aclvantageas the, radioac- :ftirni'shedswitharnechanism for bringing the source out of the i't is'expedient t' furnish the radiation detector witharco'llimator'capable of absorbing partially t'he liiaekground radiation oiffthe aerosol: sample, the collimator comprising an alphaparleabsorbingaplate withapertures. f

anks to the above-specifieddesign-features, the'prese nt nstrument exhibitshig'h sensitivity and precision, makes 'for dependable performance andoperationat convenience inundergroundmining-conditions, .andisreadilyportable. I

'.' Other'objectsandadvantages of the present "invehtion: will Become apparent-from:a;considerationof the description of an exemplary. embodiment thereof and from accompanying.

drawings, wherein: p

FIG. il isa diagrammatic illustration',fpartly in'sec'tionrof. the t resenttinstrumentyand. 1

.fFlCji. 2 is acharacteristicalphaabsorption curve of the instrument.

The instrument, accordingto the invention, comprises a casing l"('FIG. 1%), whichaaccommodates'a gasinlet conduit'Z'.

with aaport'3 closed"by-aprotective'screen (not shown in the I i This inventionfrelates to instruments .for monitoring indusdrawing), which screen supports a filter element 4 made in the by means ofmechanismS, and radioactive source'6- is brought into gas inletconduit 2. A part of the alpha particlesfrom source '6' reaches detectorB, the intensity of radiation being measured" through the agency of the electronic circuit of recorder- [*0 and indicating instrument Then mechanism 7 is actuated to withdraw radioactive source t5 frorn'gas inlet conduit 2, and the tes'tgas is drawnby rneans'of arrangement l l thr'ough filter element4 to eifectaerosol sampling. Aerosol samplinghaving been completed, radioactive source 6 is brought into conduit 2,followed by measuring for the second time the intensity of radiation that reaches detector'8 this time 7 'by passage. through filter element 4 having a dust precipitate deposited thereon. The differencehetwecn the two radiation intensity readings due to anincrease in the thickness of filter I element 4 caused by dust deposition corresponds to the weight concentrationof the aerosol .under examination.

lt ispert-inent to employ a high intensity radiation source in order toeliminate an additional error that might appear in .the results of measuring theamount of dust collected on filter cler'nent 4 said additional error bcing caused by the background 1 alpha actiyi'ty'of the dust sample obtained. However, an excessivelyhighactivityof the alpha source used would necessitate the employment ot a high time resolution electronic circuit of recorder MI in order to record the pulses fed by detector 8 and,. hence, would make the instrument recording arrangemerit excessively complicated. To avoid this limitation, the

present'instrumen't incorporates, as pointed out earlier, collimator 8 -interposed ahead of detector '8. and comprising an alpha particle absorbing plate with apertures. Thanks tothe collimator,.the count rate of detector-8 is-decreasedbyafactor of l0 ,so that, with the activity'of source 6 increased, ac-

cordingly, the amount of radiation that falls on detector 8 upon passage through the dust deposit being" examined remains unaltered, whereas the number of alphaparticles resulting from'the decay of radioactive isotopes presentin the dust sample. and reaching detector 8 would experience a l0- fold attenuation. e I

To measure the active concentration of aerosols, recourse is had todetermining'the radioactivity of the sample collected on the filtered, alpha particle source 6 being out ofagas inlet conduitZfor-the duration'ofmeasurcments. a

in view of the fact that alpha radiation has the lowest penetration power, the employment of an alpha'emitter as the radioactive source-is-condueive to recording minute changesin the thickness of filter element 4' and, therefore, renders it possible to attain high sensitivity of the present instrument despite-the use of compact arrangements '12 for pumpingthe test gas through the filter element and of a simple electronic circuit in recorder 10. Moreover, the direct relationship between the weight of the dust deposit: and the difference of the above-identified radiation intensity measurements will be observed-only within a certain aerosolparticlerange, the maximum size of aerosol particles in said range beingdependent upon the total thickness of absorbers interposed between radioactive source6'. and radiation detector 8-, as well asupon the range of alpha particles emitted by the isotope usetl...in source6. Wherea dust deposit density of, say, I mg./cm,2 is adequate for complete absorption of the energyof .an alpha particle, the alpha particle energy being also ;attcnuatcd thanks to the passage through an air layer, filter element 4 .proper and the protectivecoating of detector8', an increasein the size of aerosol particles beyond t, provided the aerosol material density equals 1 g./cm.3, does not result in a decrease of the intensity of alpha particles falling on detector 8 that would be proportional to the mass of a dust particle. i.c. to the third power of the linear dimensions of the particle in question, as in this case the absorption power would be governed by the area of the dust particle that screens detector 8 and, hence. would be proportional to the second power of the linear dimensions of the dust particle in question. The share of dust particles having a diameter of. say. L000 p. in radiation intensity attenuation would. therefore, be lOO times smaller than the weight of the particles of this size, while the dust particles under 10 p. in diameter would result in attenuating the radiation intensity proportionally to the weight of the particles in question. The employment of an alpha emitter is,

on the abscissa is the dust deposit thickness (mg./cm.2), and

on the ordinate. the intensity of radiation, N, recorded by detector 8 and expressed in pulses per second. As can be seen from the graph, the instrument performance is most effective in case the readings are taken along the linear portion a-b of absorption curve 13. The length of the linear portion a-b is governed by the ratio of the linear dimensions of source 6 and those of radiation detector 8, provided source 6 is smaller than detector 8. An adequate length of the portion a-b is attained where the diameter of detector- 8 is at least 1.5 times greater than the diameter of source 6, another condition being that the thickness offilter element 4 and that of the window of detector 8 as well as the distance between source 6 and detector 8 should be selected so that the sum total of these absorbing media would be greater than the value ma which marks the initial point a of the linear portion ab of curve 13.

Thanks to the fact that source 6, filter element 4 and detector 8 are disposed in relation to one another in the manner disclosed h'ereinabove, it is feasible to account for variations in reference to a preferred embodiment thereo the thickness of filter element 4 by measuring the radiation intensity twice, vizl, before and after. drawing the test gas through the filter element. v I I The employment of the present instrument makes it possible to measure dust concentrations of ,the order of l ing/"1.3 within 10 minutes. The present instrument seems most promising for use in conjunction with underground mining operations when it is pertinent to measure. i part from concentration of dust. also the content ofae isotopes. e.g.. short-lived products of rado Although the present invention has bee and modifications can be practiced without devi spirit and scope ofthe invention as those skilledi' readily understand.

We claim:

1. An instrument for determining the weight and active concentration of aerosols, which comprises a casing; means defining a gas conduit in said casing for sampling said aerosols; means for pumping a stream of test gas through said conduit; a filter element positioned in the conduit for the passage therethrough of the stream of test gas to collect aerosol samples; a radioactive source of alpha radiation disposed in said conduit upstream with reference to said filter element; an alpha particle radiation detector disposed in said casing on the side of said filter element opposite said radiation source; means for withdrawing said radioactive source from said gas conduit; and means for recording the intensity of alpha radiation that falls on said detector.

2. An instrument according to claim 1 wherein saidalpha radiation detector comprises a collimator constituted as an alpha particle absorbing plate with apertures whose axes are perpendicular to the surface of said detector.

3. An instrument according to claim I wherein said detector and filter element are in axial alignment. and said radiation source is coaxial therewith when operativcly positioned in said conduit. 

2. An instrument according to claim 1 wherein said alpha radiation detector comprises a collimator constituted as an alpha particle absorbing plate with apertures whose axes are perpendicular to the surface of said detector.
 3. An instrument according to claim 1 wherein said detector and filter element are in axial alignment, and said radiation source is coaxial therewith when operatively positioned in said conduit. 